﻿ Getting Started Tutorials - MechDesigner > Tutorial 11: Two Degrees-of-Freedom Planar Kinematic-Chains > Step 11.1: Piggyback Sliders as XY Table

# Step 11.1: Piggyback Sliders as XY Table

The Piggyback Slider configuration is two Sliders:

Slider(A) : moves along the X-axis of the Mechanism-Plane

Slider(B) :  mounted to Slider(A), and moves along the Y-axis of Slider(A)

The Piggyback Slider Configuration is only one way to model an XY-Path.

You can also use a Motion-Path.

The Sliders do not need to be in the X-axis and Y-axis directions or even it right-angles to each other. We describe them in these directions for convenience only.

For example, they may be in the Radial and Tangential direction relative to a radius of a circle.

#### Mechanical Systems that follow the XY Motion-Path:

Linear-Slides (Slide-ways + Slide-blocks)

The Piggyback Sliders are built in the same way as X-Y Tables that use Linear-Motion Technology (the motors and the mechanics).

The motors that drive the Sliders have the same nominal* motion as the Piggyback Sliders. See Step 11.1

* For example, a motor may rotate a Pulley to move a Belt, or a Ball-Screw to move a Nut. In each case, the motors rotate a different number of rotations, but their rotation is a linear relationship to the Slider's motion.

b.Connect Dyads between the sliders and the machine-frame.

c.Use cams or servomotors on the Machine Frame to drive the Dyads and thus the XY-table

Add motions to the Piggyback Sliders / XY-table directly. MechDesigner will use inverse-kinematics to calculate the motions for the cam-followers or servomotors - See Step 11.2

Translating Beam (a Part that moves on the Mechanism-Plane but does not rotate)

It is possible to model a translating-beam that does not physically use linear-slides.

Look at this video. This example happens to show 3 independent axes to control the motion of a Beam. In this case the motion of the beam can be specified to translate or rotate.

Use Piggyback Sliders to specify the X-Y Motion-Path, even though they are not in the mechanical system. See Step 11.3.

 Technical Note: Rectilinear Translation: All points in a Part have the same translating and parallel motions. Curvilinear Translation: All points in a Part have the same, but not necessarily straight, motions.

#### Quick Instructions: Add Piggyback Sliders

 Quick Instructions: STEP 1.Add the X-Slider to a horizontal Line in the Base-Part STEP 2.Edit the X-Slider. Add a Line that is parallel to the Y-axisSTEP 3.Add the Y-Slider to the Line that is parallel to the Y-axis of X-Slider.STEP 4.Design the motions for each Slider.STEP 5.Add a Trace-Point to a Point that moves with the Y-Slider.STEP 6.Run menu  > Cycle to watch the Piggyback Sliders.

### Degrees-of-Freedom of Piggyback Sliders

 Degrees-of-Freedom and Mobility of Piggyback Sliders Gruebler Equation to find the number of Degrees-of-Freedom (F): F = 3(P-1) – 2J  : P = Number of Parts (1 × Base-Part + 2 × Added-Parts) ; J = Number of Joints ( 2 × Slide-Joints) F = 3×(3-1) – 2×2 F = 6 – 4 = 2 Mobility = # Degrees-of-Freedom(F) – # Motion-Dimensions = 2 – 2 = 0.

### Kinematics Tree of Piggyback Sliders

 Kinematics-Tree for Piggyback Sliders. There is: •One kinematic-chain (Solved Mechanisms)The Solved Mechanism has: •Two Sliders

### Machines that use Piggyback Sliders

Example machines include:

Pen Plotters

Water-Jet Cutters

Laser Markers or Cutters

 An XY-Gantry Robot Look at the video to the left. This 'Plotter' moves a Pen along a slide, say the Y-axis slide. The X-axis carries the Y-axis slide.  The combined movement plots the drawing. With this machine, there is an EXACT linear-equivalence between the XY-Path and the control positions of the slider motors. The system is Kinematically Linear. This 'Plotter' moves a Pen with a slider along the X-axis. A different slider carries the X-axis slider, but along the Y-axis. The two movements of the slider plot the drawing.